From the most fundamental of themes, the book takes the Donne poem and applies it to the situation of Gunther's son's death. In praising the condition of the human spirit, Gunther is able to display the fortitude of courage when facing the ultimate adversary. He creates a memoir that acknowledges the power of death, but refuses to acquiesce to the force of negation. Rather, Gunther brings his son alive to us, the reader, in the face of death. In its presence, we understand how special his son was to both father and to the world. Death is not presented as a force that takes away his son's life, but rather one that causes celebration of this brief zeal that was associated with Johnny. In recognizing his son in this manner, Gunther feels that he is able to take one of the saddest images known to humanity and appropriate it in the name of his son and as a representation of a parent's love. The primary theme in this process is not to mourn the loss of life and love in the face of death, but rather treasure what is present in our own lives so that when it is taken away, no regrets will be felt nor despair experienced.
For me the theme of the book more applies to human valor and uses the brain tumor as very symbolic.